It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, dispersants, or detergents) used to protect internal combustion engines from corrosion, wear, soot deposits and acid build up. Often, such surface active additives can have harmful effects on mechanical devices (such as internal combustion engines or driveline devices). Harmful effects may include possible wear (in both iron and aluminium based components), bearing corrosion, increased acid accumulation (due to lack of neutralisation of combustion by-products), or reduction in fuel economy.
A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may also have a detrimental impact on fuel economy and efficiency and copper corrosion. Consequently, engine lubricants may also contain a friction modifier to obviate the detrimental impact of ZDDP on fuel economy and corrosion inhibitors to obviate the detrimental impact of ZDDP on copper corrosion. Other additives may also increase lead corrosion.
Other art known to a skilled person includes a number of publications disclosing esters or amides or imides of carboxylic acids, or esters or amides or imides of hydroxycarboxylic acid as possible antiwear agents. The publications include Canadian Patent CA 1 183 125; East German Patent DD 299533 A5; International Publications WO 2006/044411, WO 2005/087904, WO2008/070307; Japanese Patent Applications 2005139238 A, 10183161A, 10130679A, and 05117680A; US Patent Applications 2010/0190669, 2010/0197536, and 2010/0093573, 20050198894; and U.S. Pat. Nos. 4,237,022, 5,338,470, 4,436,640, 4,157,970, 4,863,622, 5,132,034, 5,215,549, and 6,127,327.
Detergents such as metal sulphonates, metal phenates, metal salicylates, and metal salixarates are known. The detergents may be prepared in the presence or absence of a carboxylic acid. For example carboxylic acid-modified detergents are disclosed in EP 271 262 A, EP 273 588 A, U.S. Pat. Nos. 5,792,735 and 5,674,821. Typical acids disclosed therein may be defined by the formula RCH(R1)CO2H, wherein R is a C10 to C24 alkyl group and R1 is hydrogen or a C1 to C4 alkyl group. An exemplified acid-modified detergent includes a hydrocarbyl-substituted phenate that contains 12 to 20 by weight of stearic acid. U.S. Pat. No. 3,155,617 discloses a means of activating calcium oxide (prepared from roasting calcium carbonate), so that it is useful in the methanol process for preparing dispersions of calcium carbonate. The calcium oxide is treated in methanol suspension with a small amount of an acid such as acetic acid.